There are several types or categories of sewage that have been nationally defined by the Consortium of Institutes for Decentralized Waste-water Treatment (CIDWT, 2009):
Black-water: Portion of the waste-water stream that originates from toilet fixtures, dishwashers and food preparation sinks.
Gray-water: water captured from non-food preparation sinks, showers, baths, baths, clothes washing machines, and laundry tubs. Gray water is defined in MN Rules Chapter 7080.1100, Subp 37 as; sewage that does not contain toilet wastes‘.
A Gray water system is one that receives, treats, and disperses only gray water or other similar system as designated by the commissioner (MN Rules Chapter 7080.1100, Subp. 38). Toilet wastes from the residence or other establishment have to be treated in some other system, or the residence has to have a privy.
To prevent hooking up a flush toilet onto a gray water system, the plumbing of the system must have two-inch diameter pipe, rather than four-inch. Even the floor drains have to use two-inch pipe.
The exception is for a gray water system being installed for an existing building. There is no need to re-plumb the entire structure. Gray water systems cannot accept garbage disposal waste.
Yellow water: an isolated waste stream consisting of urine collected from specific fixtures and not contaminated by faeces or diluted by gray water sources; see also urine separating device.
System Size and Factors influencing it
The amount and type of water discharged to an onsite sewage treatment system is one of the factors used in sizing that system. Other factors that influence sizing include soil properties such as texture, structure, and percolation rate.
Designing a waste-water treatment system based upon average daily flow would imply that the system is operating beyond its design capacity 50 percent of the time. For this reason, treatment systems are typically designed to produce the required effluent quality when treating the maximum daily flow. This accounts for the natural variability in the amount and strength of waste-water entering any system.
The amount of waste-water entering the treatment system is the hydraulic loading rate. In sizing for the hydraulic loading rate, the volume of water flowing through the treatment process is the design parameter under consideration. For the concept of mass loading rate, the idea of the mass or weight of a particular contaminant flowing through the system over some time is considered.
The ―organic loading rate,‖ the number of pounds or kilograms of BOD per day, and the ―solids loading rate,‖ the number of pounds or kilograms of TSS per day, are common mass loading rates.
Water use varies widely among individuals, depending on such factors as background, age and economic status. For example, an individual who was raised in a household without running water will probably be very conservative in water use even when running water is available. Teenagers are typically high water users. The use of hot tubs or water- circulating devices for therapeutic services greatly increases water use.
A number of studies have been done throughout the country on water use habits and rates. In studies done during the 1970s, average water use per person, nationwide, was about 45 gallons per day.
A 1999 study found a national water-use rate of about 60 gallons per person per day with a variation of plus or minus 40 gallons per day (Mayer, et. al., 1999). Domestic sewage is generated by a dwelling, a toilet facility at an establishment open to the public, rental units such as motels and resort cabins, shower and toilet facilities for schools or campgrounds, or anywhere typical domestic waste-water is created.
Sources of Waste-water
From some of our previous articles, the introduction of this unit and the types of waste-water listed above, you are already through with the sewage sources of waste- water. In other words, sewage could be got from domestic sewage, industrial or trade sewage and storm water (Feacham, Mcgarry and Mara, 1978; Oluwande, 1983). For this course however, industrial waste will be considered under non-sewage sources.
Domestic sewage: This is a mixture of:
Human excreta (faeces and urine, often termed night-soil, when collected separately.
Sullage – which is the waste-water from bathrooms; wash- hand basins, kitchen sink, laundry.
Industrial or Trade Sewage: industrial waste-water is the water or liquid-carried waste from an industrial process resulting from industry, manufacture, trade, automotive repair, vehicle wash, business or medical, activity that may contain toxic or hazardous constituents.
Garage floor drain liquid wastes from garages serving single and multi- family homes can consist of the following:
- Precipitation draining from vehicles and liquids from vehicle washing
- Spills from materials stored or used in the garage such as: Thinners, solvents, paints, pesticides, cleaners, etc.
- Liquids from vehicle repair such as: gasoline, used oil, antifreeze, and others.
Therefore, there is a potential for hazardous waste and other damaging waste entering the floor drain system.
Storm Wastes: This is the waste-water that arises as result of surface run-off from rain. This is of particular interest in the tropics because during the wet season, the quantity of surface run-off becomes a considerable part of sewage.
Clear water additions
Clear water (including groundwater, rainwater, surface water, condensate, ice machine drainage, and/or discharge from pools, hot tubs, and water treatment devices) fits into this category.
Sources of clear water should not be directed to the system; if connected, they can create problems in the system. A number of water-using devices (such as water softeners, iron filters and water treatment devices) do not produce sewage as defined in MN Rules Chapter 7080.
These devices do produce effluent, but that effluent has not come in contact with humans or laundry to create contamination that needs to be treated or removed. Water treatment discharge is defined by CIDWT as the by-product from a water treatment device, such as regeneration water from an ion- exchange unit; reject water from a reverse-osmosis unit, or the backwash from an iron filter.
Waters of teners reduce the number of or remove calcium and magnesium ions, which are the principal causes of hardness in water. Cation exchange resin method is most commonly used for residential and commercial water treatment. Water softener and iron filter recharge water adds a large volume of water to the system – typically 30 to 80 gallons per cycle. This is water that does not require treating.
A growing concern with water softener recharge water is that it may cause an increase in the amount of solid material that remains suspended in the liquid layer (effluent) in the septic tank and ends up in the drain field trenches or a mound.
These solids may shorten the life of the soil treatment system, increasing the chance of drain-field or mound failure. Water softener discharge has conflicting results in research studies, but it does appear that scum layers are often absent in tanks where the water softener recharge water enters the septic tank.
Iron filtersare similar to water softeners in that the effluent is not sewage, but the discharge does have different characteristics. The two choices for iron removal are ion exchange (water softener) and oxidation filtration.
Water softener is applied to water where the iron concretions are in the 2-5 ppm range. If the iron concentrations are higher (> 5 ppm) or the natural pH is high (> 8) then applying an oxidation filtration system may be more effective.
These systems physically filter the iron and then are back-flushed, removing the iron as a solid. These systems will need to be discharged into a settling component before being discharged to the soil to remove the solids that would plug the soil surface.
Reverseosmosisis a separation process that uses pressure to force water through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side.
More specifically, it is the process of forcing a liquid from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.
This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semi-permeable, meaning it allows the passage of liquid but not of solute or particles.
The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases, the membrane is designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions).
This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh and brackish water, and 40–70 bar (600–1000 psi) for seawater, which has around 24 bar (350 psi) natural osmotic pressure which must be overcome.
Reverse osmosis units sold for residential purposes offer water filtration at the cost of large quantities of waste water. For every five gallons of output, a typical residential reverse osmosis filter will send around ten to 20 gallons of water down the drain (although many people capture it and use it for watering plants and lawns). In some states this water is used for irrigation.
High-efficiency furnaces operate at a high efficiency and therefore save on energy use. One of the results of the heating process is that condensation occurs in the unit. When this condensation builds up, water slowly trickles out of the unit and into the plumbing that is often connected to an onsite system. The water can cause freezing problems in the onsite system because of the slow, steady flow.
In addition, this water is clean and therefore does not need to be treated. When the furnace is in operation, this water typically trickles out of the unit at a volume of five to ten gallons on a cold day. In high-efficiency furnaces, the recharge water from water softeners and iron filters has the potential to cause problems with onsite sewage treatment systems.
Domestic sewage is also generated by other establishments. Another establishment‖ is any public or private structure, other than a dwelling, that generates sewage and discharges it into a public drain system or sewage. Other establishments may have large flows and/or high-strength waste.
Non-domestic waste is generated by many sources, such as restaurants, laundromats, barber shops, car washes and other light industrial establishments. Waste other than sewage is only allowed to be discharged into the sewage system if the waste is suitable to be discharged to groundwater. If waste strength parameters exceed the values identified in MN Rules Chapter 7081.0130, Subp. 2, the system should include pretreatment.
A range of systems can be designed for other establishments.
Type I: if domestic levels of waste-water can be achieved with septic tanks alone the system is classified as at Type I system.
TypeIIor III: if site or soil conditions are limiting.
Type IV: if the system uses a registered product (Treatment Level C) to reduce waste strength the system is considered to be a Type IV system.
Type V: if the system uses a non-registered product to reduce the waste strength the system is consider to be a Type V system.
Some ―other establishments‖ include the following:
1. Apartment buildings
Rental situations have been known to have overuse of the system. The renter may not understand the impacts of their usage habits on the system and may have little concern about over using water.
Multiple families can also impact the loading to the system. Low-flow fixtures and appliances along with education can assist in the management of the system.
Day cares are always going to have higher flows associated with their use. The other concern here will the cleaners that are used and the type of food that is available.
In-home day cares will have higher flows than are typical for the number of bedrooms in the house due to the amount of people that are in the home and the amount of time they are there.
The kitchen or waste strength will be similar to a normal home. The use of cleaners must be watched in these systems. Excessive cleaning, which is common in day cares, can lead to the killing of the bacteria and lower efficiency in the treatment tanks.
3. Commercial kitchen
A commercial kitchen is a food preparation center that prepares multiple meals or food products and typically generates high-strength waste- water.
The food service waste-water from these facilities is non-toxic, non-hazardous waste-water and is similar in composition to domestic waste-water, but which may occasionally have one or more of its constituents exceed typical domestic ranges.
It includes all the sewage wastes from commercial food preparation, food processing or food production sources.
Restaurants and bars almost always have high-strength waste that makes sewage treatment difficult. For this reason, a number of best management practices can be taken to facilitate treatment:
- Limit food particles and alcohol going down the drain
- Limit the use of chemicals going down the drain: chemicals can kill the treatment system‘s good bacteria
- Limit use of degreasers, even in cleaning supplies
- A grease interceptor, a watertight device designed to intercept, congeal and retain or remove fats, oils, and grease (FOGs) from food-service waste-waters; may be located inside (grease separator) or outside (grease tank or grease trap) of a facility that generates commercial food service waste-water
- Isolate kitchen waste from other sewage production
- Design tanks for a minimum of four to seven times the daily flow
- Be aware that high water temperatures (140°F) do not allow grease to solidify, adding to treatment concerns
- More tanks in series can help cool effluent
- Be aware that septic tanks alone usually will not get the job done.
In conclusion from our discussions above, we can conclude that waste-water is a collection of sewage and non-sewage liquid matter which originates from homes (from human and domestic activities), industries, and storm water etc.
These are not friendly to human being because they are rejected and until when treated for reuse and or disposed off, man will not rest. Knowing their components or types and sources will help in handling them properly to avoid harming man or his environment.
The types of waste-water according to the Consortium of Institute for Decentralized Waste-water Treatment (CIDWT, 2009) include black- water, gray-water and yellow-water.
The system, sizes and factors influencing it were learnt and they included: amount and type of water discharged to an onsite treatment system, soil properties like texture and structure and percolation rate. Sewage waste source was discussed and they come from domestic activities like washing, kitchen sink, bathing, faeces and urine etc.
Non-sewage source was equally discussed and these include clear water addition, water softeners, reverse osmosis, and industrial waste etc.
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